Letter Tile Possibilities - LeetCode solutions

Problem

You have n tiles, where each tile has one letter tiles[i] printed on it.

Return the number of possible non-empty sequences of letters you can make using the letters printed on those tiles.

Example 1:

Input: tiles = "AAB"
Output: 8
Explanation: The possible sequences are "A", "B", "AA", "AB", "BA", "AAB", "ABA", "BAA".

Example 2:

Input: tiles = "AAABBC"
Output: 188

Example 3:

Input: tiles = "V"
Output: 1

Constraints:

1 <= tiles.length <= 7
tiles consists of uppercase English letters.

Solution (Java)

class Solution {
    private int count;

    public int numTilePossibilities(String tiles) {
        count = 0;
        char[] chars = tiles.toCharArray();
        Arrays.sort(chars);
        boolean[] visited = new boolean[chars.length];
        dfs(chars, 0, visited);
        return count;
    }

    private void dfs(char[] chars, int length, boolean[] visited) {
        if (length == chars.length) {
            return;
        }
        for (int i = 0; i < chars.length; i++) {
            if (visited[i] || i - 1 >= 0 && chars[i] == chars[i - 1] && !visited[i - 1]) {
                continue;
            }
            count++;
            visited[i] = true;
            dfs(chars, length + 1, visited);
            visited[i] = false;
        }
    }
}

Explain:

nope.

Complexity:

Time complexity : O(n).
Space complexity : O(n).